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# Pygame Intro
## Making games in python
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# Problem

You want to create a game but you don't want to write your own
--

* graphics library

* audio library

* user input library

* deal with the quirks of each operating system

Don't worry there's `pygame`. A good python wrapper around SDL so you don't have to worry about those things.
---

# Getting Started

We're going to cover the following things in this lesson

* Window Creation

* Drawing Things

* An deeper look at screen rendering

* General Game Structure

---

## Window Creation

```python
#!/usr/bin/python

import pygame

pygame.init()
width = 600
height = 300
screen = pygame.display.set_mode([width, height])
while True:
    # It's okay if you don't know what this does I'll get to 
    # this call. But it's important to have at the end of 
    # your render loop
    screen.flip()
    continue
```

`screen` here is an SDL surface. Pretty much everything you draw is a surface

surfaces are associated with a specific pixel map / image

???

Here we just have the height and width passed in  
There are various flags you can use like HWSURFACE and the double buffer flag  
This is just draw a window but there's nothing in it yet

That's it. Now you have a window!

---

# Drawing things

This is only slightly more complicated

```python
#!/usr/bin/python

import pygame

pygame.init()

height = 300
width = 600
screen = pygame.display.set_mode([width, height])
# The convert call is not strictly necessary
ball = pygame.image.load("../resources/ball.png").convert_alpha()

# Surfaces are "blit" or "drawn" to other 
# surfaces in this case the screen
screen.blit(ball, (0, 0))
while True:
    pygame.display.flip()
```

???

Everything is pretty much the same  
the ball is loaded from a resource file in a sibling directory  
the convert alpha call is important mostly for speed  
get into the habit of using convert if you want things to move quickly  
there are various blending modes for surfaces but I'm not going to get into those

An "object" on the screen is really a combination of a rect/location on the source and an image

questions?

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# Screen Rendering / Double Buffering

The screen doesn't clear automatically  
--

We have a couple of options:  
--
    1. Overwrite everyting on the screen with a background color each frame  
--
    2. Make sure you redraw the seconds of the screen that move/change  
--

Number 2 would involve a lot of specialized optomization and we don't need to
bother with that right now

Now we have a new problem:    
Clearing the screen can create flickers

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# Problem (the flicker)
## Immediate Mode

When you draw something to the screen it gets put there right away

???

For a split second just the objects that have been drawn are on the screen
The entire screen is updated on every draw  
You clear the screen, you'll see it for a few milliseconds  
You draw a ball you'll see the ball on the black screen for a few milliseconds  
You draw a cat you'll see the ball and the cat on the black screen for a few milliseconds... etc.

This is fast but causes the flicker when things disappear

What is the solution for this?

---

# Fix (Buffering to the rescue)

Don't draw directly to the screen

Draw to a buffer that get displayed at once

No flickering because the screen is only cleared by overwritting it with
a completed image

This optimization is so simple it's enabled by default so, no work for you!

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# Game Structure

Initialization

Game Loop

1. State(managed by FSM, possibly multiple levels)
    2. Game Logic
    3. Rendering

Cleanup

???

Show breakout demo

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